In reply to Sam29:
first off, i havne't climbed the route yet, but doing it in July so I'm gathering a lot of beta myself...so i could be wrong on this, but so far this is what i've managed to figure out
yes annual snowfall in the winter is considerably more during those months, making progress by walking difficult. there will also be unstable weather patterns during this period, what sort of window do you have for making your bid? I would recommend at least a week, two would be more suitable.
the hill is very very steep from the cable car to the bottom of the route. there is a very informative video on youtube if you search aiguille du midi. its by a yank, and he is climbing but not on the arete, though you'll get so good info from this. i wouldn't have thought ski-ing it would be possible.
as with most alpine routes, i'd imagine this would be a much more serious undertaking in the winter compared with summer, i'd say add two grades. have you done simmilar, like winter asecnt of tower ridge etc?
hope that helps and doesn't come across as trying to put you off - thats not the intention! please let me know how you get on. and good luck. cheers.